4 CIRCULAR 6 2 7, U. S. DEPARTMENT OF AGRICULTURE 



Verner (60) described a different type of pressure tester for use with 

 stone fruits, in which the fruit is squeezed between two flat surfaces 

 or disks for a given distance. A modification of this instrument 

 (fig. 2) has been used to test the firmness of strawberries (28, 56) also. 



METHODS OF MAKING PRESSURE-TEST 

 DETERMINATIONS 



With apples and pears it is customary to make 2 or 3 tests on each 

 fruit at about equal distances around the periphery and midway 

 between the stem and calyx ends. With peaches 2 tests, 1 on each 

 cheek of each fruit, have generally been made (14, 31, 42). Culpepper 

 and Caldwell (17), using a needle plunger, made 10 tests on each 

 peach: 6 on the cheeks, 1 at each end, 1 at the suture, and 1 opposite 

 the suture. Blake and Davidson (10) made 12 tests on each peach: 

 1 on each cheek, 1 at the suture, and 1 opposite the suture, at each of 

 3 points on the fruit — the top (stem end), the middle, and the apex. 

 Coe (14) varied the point of pressure testing somewhat from season to 

 season; but in the last season of his investigations he made the tests 

 on the cheeks, as the suture became too soft for a reliable measure of 

 firmness and did not represent the position most subject to bruising. 



Magness and Taylor (48) showed that the skin of apples may mask 

 the firmness of the flesh. They recommended that the skin should 

 be sliced oft at the points to be tested, and this is the customary 

 practice with both apples and pears. With peaches also, the skin 

 was removed before testing by Magness and Allen (42) and by Harding 

 and Haller (31). Coe (14) and Blake and Davidson (10) made tests 

 on both the peeled and unpeeled fruit but based their recommenda- 

 tions on tests with the peel intact. Morris (51) also tested peaches 

 without peeling them. Blake and Davidson (10) observed that 

 tests through the skin required less time, and they considered it 

 desirable to test through the skin, because skin texture as well as 

 flesh firmness may be a factor in the capacity of a peach variety to 

 withstand handling and shipping. They found that the skin offered 

 less resistance to puncturing when the peaches were soft ripe than 

 when they were shipping ripe. This is contrary to results with apples, 

 in which Magness and Taylor (48) found greater resistance to pene- 

 tration through the skin in the riper fruit. Although skin texture 

 may be important in comparing peach varieties, it seems likely that 

 flesh texture would be most important in following the softening 

 changes within a variety in relation to maturity or ripening, and 

 therefore it would be desirable to remove the peel from peaches as 

 well as from apples and pears before making pressure tests. 



A plunger % 6 of an inch in diameter and with a penetration of % 6 

 of an inch has been used with apples. A plunger with the same 

 depth of penetration but with a diameter of only %e of an inch has been 

 used with pears. Generally, a plunger of the same size and depth of 

 penetration has been used with peaches as with pears. However, 

 Blake and Davidson (10) used a pressure tester in which the plunger 

 rod extended through both ends of the barrel and it was necessary 

 to hold the tester by the side; consequently, it was found desirable 



